This invention relates to photographic systems. More particularly, it concerns a method and apparatus for storing, exposing and processing photographic film from which a positive print or transparency is formed by exposing an initially separate negative sheet and bringing the negative into face-to-face contact with a positive image receiving sheet previously coated or impregnated with a processing agent capable of effecting image transfer from the exposed negative to the positive receiver.
Commonly assigned U.S. Pat. No. 3,907,563 issued to Edwin H. Land on Sept. 23, 1975 discloses a diffusion transfer process in which the image receiving element or sheet is impregnated with an alkaline processing composition. The image receiver or positive sheet includes a transparent support through which the final image may be observed in an image receiving coating or layer directly on the transparent support. Reflectivity for use of the system as a positive print is provided by a white pigmented layer backed by an opaque layer. The three layers thus provided on the transparent support are impregnated with a liquid alkaline processing agent common to diffusion transfer film processing.
The negative element of the system disclosed in the aforementioned patent includes a support of mylar or similar material which may be either transparent or opaque. The negative support is coated by polymetric acid layer, a timing layer, a dye developer layer and finally a silver halide layer. After exposure of the silver halide layer on the negative, the two sheets are brought together in intimate face-to-face contact as a laminate with the several coatings situated between the respective negative and positive sheet supports. The processing agent functions to transfer the latent image formed by exposure of the silver halide layer of the negative to the image-receiving layer directly behind the transparent support of the receiver sheet. The acid layer in the original negative sheet functions to neutralize the alkaline processing fluid but under the control of the timing interlayer situated between the acid layer and the remaining layers of the composite laminate.
The diffusion transfer system disclosed in U.S. Pat. No. 3,907,563 is especially attractive from the standpoint of attaining high quality photographs with virtually no provision for assuring uniformity of processing fluid spread between the respective negative and positive elements other than impregnation of the positive element during manufacture. In this respect, it is to be noted that in substantially all commercially available diffusion transfer film systems, the alkaline processing fluid is initially contained by a rupturable pod, carried as a component of the film assembly, to be spread between the negative and positive elements of the film assembly after negative exposure. The uniformity of this spread requires precision not only in the processing apparatus which is incorporated as a part of a camera or equivalent, but also a sophisticated and expensive combination of elements in the film sheet assembly, itself.
While a film system of the type disclosed in U.S. Pat. No. 3,907,563 has potential for significant reduction in costs over current diffusion transfer systems particularly in the manufacture of film, use of such film on a commercial basis is not without problems. Because of the strongly alkaline character of the processing agent and the need for its neutralization after processing, the components carrying the processing agent and the neutralizing acid layer must be kept separate until the processing step is performed. Also, it is important that the liquid processing agent in the positive sheet element be kept from evaporization and that the pH level of the liquid be maintained. Moreover, these conditions must be maintained not only for the normal shelf life of commercial photographic film but also after the film is loaded into a camera and stored in the camera. In addition, the film system requires an image reversal prior to negative exposure because the positive image observed through the transparent support on the receiving element is identical to the image received on the negative. In other words, a reflux mirror is required between the lens and the film plane of the camera in which the film is to be exposed.
Commonly assigned U.S. Pat. No. 3,314,792 issued to Edwin H. Land on Apr. 18, 1967 discloses a camera system for accommodating photographic film in which a processing liquid is impregnated in or coated on one of two sheet elements. In this instance, the negative and positive sheet elements are separately packaged and thus separately mounted in the camera in order to solve the problem of sealing the processing the liquid impregnated component of the film system to maintain the pH level of the processing liquid and also to prevent its drying out. Other prior U.S. patents which address this problem include U.S. Pat. No. 3,229,605 and No. 3,238,858 issued to V. K. Eloranta and No. 3,314,791 issued to E. D. Cotta et al. None of the disclosures in any of these patents, however, have been incorporated in a viable commercial photographic system.
In light of the foregoing, it will be appreciated that there is a need for a photographic system by which the significantly reduced manufacturing costs of processing fluid impregnated film units may be advantageously deployed.